Increased flexibility means less exercise-related muscle damage, according to one study.
Every runner is familiar with the experience of waking up sore the morning after a hard run. Such soreness is largely related to muscle damage caused by eccentric (pronounced ee-sentric) strain on muscle fibers. Eccentric strain occurs when gravity and/or an external force pulls on a muscle and tries to lengthen it while the muscle itself resists this pulling and tries to shorten. A good example of eccentric strain is that which the biceps muscle group experiences during the lowering phase of a dumbbell curl. The dumbbell pulls your hand toward the floor, forcing your biceps to lengthen, while your biceps resists this lengthening to control the speed of the dumbbell’s descent.
There’s lots of eccentric strain in running, too. For example, the quadriceps muscles experience eccentric strain during the stance phase of the stride. When your foot lands on the ground, gravity tries to make your whole body collapse in a heap. To prevent this from happening, your quadriceps must contract to keep your knee from buckling, but at the same time your quads must stretch a bit to absorb impact. Thus, the muscles are pulled in two directions at once and some of the individual fibers suffer microscopic tearing under the strain.
The best way to increase your tolerance for eccentric strain in running is to run. Practicing fast running and downhill running is especially effective in boosting eccentric loading tolerance. But a 2010 study by Taiwanese researchers suggests that stretching may also help, at least with the eccentric strain of weightlifting. Thirty untrained subjects were divided into three groups. For eight weeks, one group performed static stretching three times per week, a second group performed proprioceptive neuromuscular facilitation (PNF) stretching three times per week, and a third group did no stretching. Before this eight-week period and again at the end of it, all three groups performed “lengthening contractions” of the hamstrings (the lowering phase of a hamstrings curl) and the resulting muscle damage was measured.
The researchers found that both types of stretching increased range of motion at the hip joint significantly (25 degrees on average), while members of the control group exhibited no change in flexibility. Both types of stretching also significantly reduced muscle damage and soreness caused by the lengthening contractions of the hamstrings, reduced the amount of hamstrings strength lost after the workout, and accelerated the recovery of hamstrings strength.
So there you have it: Both static and PNF stretching appear to increase the hamstrings’ tolerance for eccentric loading in a weightlifting exercise in untrained subjects. Does this mean that stretching also increases tolerance for running-induced eccentric strain in the quads, hamstrings and calves (all of which muscles experience eccentric strain in running) of trained runners? This question remains to be answered.
The relationship between stretching, flexibility and running performance is complex. For example, stretching immediately before high-intensity running has been shown to lower running economy and reduce performance. Running itself naturally increases the stiffness of certain tendons and thereby enhances running economy, essentially by enhancing the ability of the legs to function like springs. On the other hand, stretching is an effective means of reducing the risk of particular running injuries (such as IT band syndrome) and abnormally tight muscles are known to limit the running stride and performance (elite runners tend to be more flexible in the hips than average runners).
Given all of this, what is a runner to do with respect to stretching? I believe that runners should have at least normal range of motion in all of the major joints, and should stretch to increase the elasticity of any tight muscles that limit their range of motion. For example, like a lot of runners, I have very tight hip flexors that shorten my stride by constraining my hip extension, so I stretch my hip flexors daily.
The thing runners need to avoid is laxity in the major joints. Lax joints cause energy waste during running. Stretching has the potential to create excessive laxity in the joints, but I think you can easily avoid this problem simply by running (which again, stiffens the tendons) a lot more than you stretch. Incorporating regular functional strength training into your regimen will also help. Strength training further increases the stiffness (hence springiness) of the legs during running, but if approached correctly, it does so in a way that actually increases functional range of motion at the same time. For example, performing giant walking lunges with dumbbells will make your hamstrings strong throughout their entire length continuum, increasing your flexibility at the hips while increasing the overall stiffness of your stride.
Indeed, while strengthening and stretching are generally thought of as being opposing actions, they can actually be combined quite easily, and the most beneficial types of stretching for runners are probably those that include a strengthening component, such as PNF stretching, functional strength exercises such as giant walking lunges, and yoga.
About The Author:
Matt Fitzgerald is the author of numerous books, including Racing Weight: How To Get Lean For Peak Performance (VeloPress, 2012). He is also a Training Intelligence Specialist for PEAR Sports. To learn more about Matt visit www.mattfitzgerald.org.